Circuit breakers are well-known devices used to provide automatic circuit interruption, to a monitored circuit, when circuit fault conditions occur. Fault conditions include, but are not limited to, current overload, ground faults, over voltage conditions and arcing faults. The release or disengaging of circuit breaker contacts to interrupt a monitored circuit is commonly referred to as tripping. The current interruption is usually achieved by having a movable contact (attached to a movable blade) that separates from a stationary contact (attached to a stationary blade). The movable contact is under considerable spring tension to move away from the stationary contact to open the circuit. When the movable contact separates from the stationary contact, it is important that this physical action occurs quickly and reliably to minimize arcing. If the arcing is too intense, it can affect the ability of the circuit breaker to open the faulted circuit. It is also important, in the design of circuit breaker trip mechanisms, that the force required to trip or open the circuit breaker mechanism is minimized.
In typical circuit breakers a latching mechanism is used to provide engagement of the circuit breaker contacts. When the circuit breaker contacts are closed or engaged, the latching mechanism holds the spring-loaded circuit breaker contacts together, and thus must resist the considerable spring force that causes the circuit breaker contacts to open when the latch is released. At the same time, the latching mechanism must be sensitive enough to trip and open the contacts with minimal force.
One of the disadvantages of many latching devices, is that the required sensitivity of the tripping mechanism makes them liable to inadvertent tripping due to shock and vibration. One of the sources of local shock vibrations is the actual act of manually closing the circuit breaker contacts. Since the breaker contacts must be closed as rapidly as they are released, the snap of closing the circuit breaker contacts sets up a shock vibration within the circuit breaker unit itself. This local vibration can cause an immediate nuisance trip. Therefore, various design solutions can be used to stabilize the breaker mechanism against shock and vibration forces. These designs, however, typically require greater energy to perform the intended trip function, which is undesirable.